not so slammed

Discuss light weight issues concerning road bikes & parts.
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Calnago
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Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

Slack seat tubes and steep headtubes are not compromises when designing a bike for a tall person. They are totally the right things to be doing as bikes get larger. Versus the very small frames where compromises abound around 700c wheels. They have to slacken the head tube angle from the ideal for that size in order to get the front wheel far enough in front to avoid extreme toe overlap. Chainstays which would be better shorter are difficult due to ending up with too long a front center relative to the back, making for awkward handling. And now with discs and 135mm rear dropout spacing, short chainstays which would be better for the small road frame, will now compromise drive train efficiency even further. Drivechain manufacturers have specified longer minimum chainstays lengths for disc brakes bikes which, for a larger bike (even one my size) where the chainstay length is generally going to be longer than that anyway, theres no problem. But for the smallest bikes, you’re really compromised at both ends of the bike. Hence the period of time when 650 wheels were popular for custom small frames and many production frames. I guess the market just wasn’t big enough for that however and it was always a chore to find the the necessary tubes and tires etc. being readily available. The really big bikes of course look awkward but at least geometry doesn’t have to be compromised. However, simply due to how long some of the tubes become, they can sometimes be pretty flexy without building with much heavier tubes. I’ve certainly owned a couple bikes in days gone by that fall into that category.
Last edited by Calnago on Fri Jul 12, 2019 6:34 am, edited 1 time in total.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

by Weenie


WorkonSunday
Posts: 119
Joined: Tue Jan 16, 2018 4:39 pm

by WorkonSunday

agree with Colnago. my wife is 158cm in height and her bike always struggles with even standard size water bottle.

i believe Emma Pooley (ex-GCN presenter) also has the same problem with 700c wheels. in her first few videos, she explained she much prefers 650c and had a custom bike build to a super short headtube in order to use 700c comfortably.

since the popularity increases in disc brake bikes, my wife now uses a 650b on her bikes (both her MTB and A1r are 650b).
In the house: Colnago V1r, Colnago A1r, Wilier Cento1 Air, Scott Scale 700SL, Bianchi FSE, Colnago Concept, Colnago A1r, Specialized Ruze Pro, Wilier GTR, Argon 18 E117 Tri+, Brompton B75

TobinHatesYou
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by TobinHatesYou

Wheelbases aren't increasing proportionally to rider height on larger (or smaller) bikes. A 62cm Emonda has 1010mm wheelbase while a 54cm has a 981mm wheelbase...a 3% increase. The average rider on a 56cm bike is probably 5'10" whereas someone on a 62cm is probably 6'4"...an 8.5% increase. Taller riders have their asses closer to the rear axle and their shoulders closer to the front axle. This is fine on flat ground, but not great when the road starts to tilt.

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Calnago
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by Calnago

That last post doesn’t make much sense to me, but so be it. Dimensions don’t need to change proportionally to ride height. Rider weight, center of gravity and balance between the wheels is far more important. Far easier to manipulate larger frames’ angles and tube lengths accordingly than it is for the very small bikes, at least under the constraints of 700c wheels. I doubt there’s a frame builder around who wouldn’t concur that very small frames create the most challenges.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

TobinHatesYou
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by TobinHatesYou

When the road tilts up, a tall rider's CoG will shift rearward more dramatically due to the relative wheelbase. If you need a better way to visualize the issue, just imagine an even more extreme case. pretend the rear axle is even closer horizontally to the saddle position.

I agree that small bikes have their own separate issues. Toe overlap, bottle cage issues, etc. but CoG isn't really one of them. 650b helps a lot. Conversely larger wheels and wheelbases on frames 62cm and above would also make sense.

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Calnago
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by Calnago

As a taller rider I don’t find that at all. I can say I hate really short chainstays, probably for that very reason. Yet I get why a small person would welcome them. My chainstays are a reasonable 412-415mm. At that length I don’t feel a rearward center of gravity at all. It’s jussst right. And the thing about larger frames is that unless they’re really really big, larger wheels are not something I would even consider. Certainly not for a 62cm frame for sure. Unlike small frames where a 700c wheel really does create challenges for the frame builder. But now I’m just repeating myself. And it’s easy to make wheelbases longer as needed on larger bikes. But it’s extremely challenging to make wheelbases useably shorter on small bikes.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

TobinHatesYou
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by TobinHatesYou

If you lenthen the chainstays you inevitably have to make them shallower in order to keep BB drop manageable. The strength of the rear triangle is further compromised the more it deviates from equilateral. This is compounded by the rear triangle being innately weaker as it increases in area. Maybe it's manageable with a 60-62cm, but I think there's a pretty good reason why manufacturers have pretty much stopped making 64cm frames...maybe that's the tipping point.

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Calnago
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by Calnago

Now you’re just making stuff up again. Of course the BB drop gets managed as chainstays get longer. So what. Nite nite. Trying to catch up on the Tour as I had to record it. The reason there are few super large frames has nothing to do with difficulty in making them and everything to do with demand.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

TobinHatesYou
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by TobinHatesYou

Or did I Google it?! Triangles get weaker the larger they get. Triangles are stronger the closer they are to equilateral. None of this is made up. This is why on some large specialty bikes you see additional tubing to turn large triangles into two smaller ones. This is why larger wheels would alleviate some of these issues in a small way...increased BB drop means the rear triangle can be strengthened via geometry.

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Calnago
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by Calnago

So you use thicker walled tubing. Stronger layups. Etc. Like Specialized likes to say “rider first” engineering or whatever they call it. Nothing new, just using the appropriate layups to give the required strength for the size of the frame. Now go back to googling. At least sometimes the regurgitations are correct versus the stuff you try to make up all by yourself.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

TobinHatesYou
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by TobinHatesYou

Calnago wrote:
Fri Jul 12, 2019 8:07 am
So you use thicker walled tubing. Stronger layups. Etc. Like Specialized likes to say “rider first” engineering or whatever they call it. Nothing new, just using the appropriate layups to give the required strength for the size of the frame. Now go back to googling. At least sometimes the regurgitations are correct versus the stuff you try to make up all by yourself.

More composite layers would likely have adverse effects on compliance. Larger diameter tubes as well. In an ideal world, the solution is a mix of everything...a couple more plies in the composite, maybe larger diameter tubes, increased chainstay length, more BB drop, larger wheels. Modern bikes are still for the most part designed around the medium sizes no matter what they say about "Rider First Geometry" and stuff like that. Nothing you say is going to change the fact that concessions are made in both large and small frames because they can get away with it.

Kind of like how a 62cm Venge weighs the same as a 62cm Tarmac SL6. They had to add way too much material to the 62cm SL6 while maintaining the same overall cross-section as the smaller sizes. As it turns out the larger diameter tubes in the 62cm Venge provides the needed strength in the middle of the tubes without the added thickness.

ancker
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Joined: Sat Dec 31, 2011 9:29 pm

by ancker

Slammed stems almost always look better.
But a manufacturer has to make frames that work for everyone. 48->61cm usually in 2cm increments.

Even the Pros aren't robots with perfectly proportioned limbs. So I do expect that a decent percentage of them have a 5-10mm spacer under the stem to get the best fit on their otherwise correct sized frame. This is magnified since all of them ride sponsored bikes. It might be that a rider would fit better (no spacers) on another frame, but the sponsor dictates what frames they have available ride, not the rider.

SilentDrone
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Joined: Fri Sep 22, 2017 5:55 pm

by SilentDrone

AJS914 wrote:Thansk.

The problem with big frames is when the rider can't find a frame big enough or they have long legs and shorter torso/arms. They end up with too much seatpost, too many spacers and an upward sloping stem. It generally looks horrible. These guys probably need a custom frame.

Image
The main problem here is that this rider is constrained to have 700c wheels. If there was a larger standard size available the frame could be built around those to accommodate his height. IMO, we’ll never see that because there aren’t enough tall people as customers to warrant anyone manufacturing for this, and I double [sic, doubt] we’ll ever see a 6’7”+ pro at the highest level because the math doesn’t work for such a human body- ie power/weight ratio, aero drag, etc.


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Last edited by SilentDrone on Fri Jul 12, 2019 9:43 pm, edited 1 time in total.

SilentDrone
Posts: 201
Joined: Fri Sep 22, 2017 5:55 pm

by SilentDrone

I’m 6’4” and here’s my Domane 62cm. One reason I don’t use deep aero wheels is because the depth combined with the rotor makes the wheel look tiny on a bike like this, making the proportions worse.

In person and shot from the right angle it’s not too bad, I think...

Image

Most pic are not flattering, but I love it for what I can do with it. There’s no sense in hating since I need it for the fit.

Image








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TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

SilentDrone wrote:
Fri Jul 12, 2019 9:43 pm

The main problem here is that this rider is constrained to have 700c wheels. If there as a larger standard size available the frame could be built around those to accommodate his height. IMO, we’ll never see that because there aren’t enough tall people as customers to warrant anyone manufacturing for this, and I double well ever see a 6’7”+ pro at the highest level because the math doesn’t work for such a human body- ie power/weight ratio, aero drag, etc.

Yep, and if you simply extend the wheelbase, the chainstays will have to run shallower and the rear triangle will open up. It’s a structural challenge that can be helped slightly with larger wheels and BB drop.

Decreasing BB drop increases CoG vertical to the wheel axles also. This will affect stability at least a little bit even if BB height is consistent with smaller sized frames.

It’s a lot of small percentage changes that add up. Bike sizing is one of those situations where I am pretty glad to be of average height.

by Weenie


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